One type of prior art device utilized to apply coatings to workpieces is a rotary atomizer. Such a device is particularly useful in coating large surfaces in high volume such as the painting of automobile bodies and the like. A disk or a bell is driven in rotation by an air-powered turbine motor. Paint is delivered to the inner surface of the disk or bell and is thrown off in small particles through centrifugal force. Typically, the surface of the bell is charged to a high voltage normally between 30 KV and 125 KV to electrostatically charge the paint particles.
One form of rotary atomizer is disclosed in U.S. Pat. No. 4,555,058. This device has a bell which is rotated at high speeds, normally between 10,000 and 40,000 rpm. The rotary bell has a plurality of paint openings formed therein connected to a source of paint. Air under pressure is forced through another plurality of openings in a front plate to direct shaping air over the outside of the bell to thereby shape the stream of paint particles exiting from the bell and direct them toward the object to be painted.
U.S. Pat. No. 4,423,840 discloses an ultra high-speed rotary atomizer bell designed to eliminate foam or bubbles in the applied coating. As the bell is rotated at high speed, centrifugal force causes the paint to flow through distribution apertures to a generally conical interior flow surface on the discharge side of the bell. Centrifugal force also causes the paint to flow along the conical interior surface in a continuous film to a sharp discharge edge between the conical surface and the front end of the bell. The front end of the bell has a predetermined wall thickness and forms a sharp discharge edge at the interior surface and is rounded at the exterior surface. By rounding the discharge end on the exterior surface, the entrapped air or other cause of bubbles in the applied coating is eliminated, even though the rotary atomizer bell is operated at extreme speeds which may be on the order of 40,000 rpm, or more.